Spike synchronization of tympanic receptor fibres in a grasshopper (Chorthippus biguttulus L., Acrididae)

In recordings from single tympanic receptor fibres in C. biguttulus, the response to synthesized sounds (rectangularly modulated white noise) interrupted by very brief (a few milliseconds) gaps was examined. In behavioral tests, females of the species respond very differently to such 'model syllables' at moderate intensities, depending on the gap width. If the gaps (in a moderate-intensity syllable) are larger than 2 ms, the stimulus fails to elicit a response, whereas stimuli with gaps smaller than 1 ms are as effective as uninterrupted syllables (D. von Helversen 1972; O. von Helversen 1979). Neither the mean spike count nor the interspike-interval distribution of the single receptor response contains the information sufficient to distinguish uninterrupted syllables from syllables with gaps. On the other hand, examination of the temporal distribution of the spikes reveals that gaps (or the pulse onsets following the gaps) cause spike synchronization. An index of synchronization (IS) was defined as a measure of this gap-induced effect. Analysis of the receptor responses based on IS revealed differences that correspond quantitatively to the abrupt abolition of the behavioral response at a gap-width between 1 and 2 ms. From the hypothesis that such brief gaps are detected by the nervous system by way of spike synchronization in the tympanic nerve, one can predict certain features of the behavioral response to high-intensity stimuli. The gap-induced spike synchronization was more pronounced at higher temperatures. This effect was demonstrated in both summated recordings from the tympanic nerve and single fibre recordings. Experiments with primary auditory fibres of Locusta migratoria showed that the receptors in this species respond very similarly to the same stimuli. That is, the receptors of C. biguttulus are not specially adapted for detecting very brief gaps. Synchronization of the spikes in parallel receptor fibres of the tympanal nerve is probably a general feature of acridids; we infer that in C. biguttulus this gap-induced synchronized activity is detected by special processing in higher auditory centres.     

Endodermal secretion of chitin in the 'cuticle' of the earthworm gizzard

The gizzard of earthworms is definitely of endodermal origin. Contrary to the opinion that tissue of endodermal origin is unable to synthesize chitin, the gizzard epithelium secretes large amounts of chitin-containing material which has special properties. 28.7 +/- 5.7% of the dry weight proved to be chitin; the microfibres form a random felt-like texture. They are not arranged in layers comparable to those found in arthropod cuticle. The protein content amounts to 44.9 +/- 7.1% of the dry weight; the remaining material contains at least uronic acids. In the protein matrix large amounts of the enzymes amylase and protease have been demonstrated. As the so-called cuticle is sloughed off at the lumen side, these enzymes are mingled with the gut contents. It might be called a gastric shield, as it closely resembles this structure, widespread among Mollusca. The thickness of the gizzard cuticle varies between 10 and 90 mum in Lumbricus terrestris and 10-50 mum in L. rubellus. Autoradiography has shown that it is replaced at a high rate. In Lumbricus terrestris it is renewed completely in less than 60 hr, and in smaller Lumbricus rubellus, this takes place in about 48 hr. These results are in agreement with the biochemical findings.     

Evolution of social parasitism in ants

Slave raids of Amazon ants, the beheading of the host colony's queen by a parasitic Bothriomyrmex female, or the protracted throttling of the host queen by an Epimyrma female which has penetrated a Leptothorax nest, are among the most intriguing behaviors to be observed in social parasitic ants. The evolutionary origin of these behaviors, however, is quite obscure, and further work is needed to elucidate how parasitic life cycles could have arisen from the ordinary social organization of ants.     

The peculiarities of Blastocrithidia triatomae

Blastocrithidia triatomae parasitizes triatomine bugs, the vectors of Chagas disease. Co-cultivation with a host-derived cell line permits continuous culture but the host cells are destroyed. Removal of the reduviid cells induces the formation of drought-resistant cysts, but the factors that induce encystment are unknown. Excystment is triggered after the onset of blood digestion in the insect host, a transition that is associated with unusual ultrastructural alterations. Günter Schaub, Dagmar Reduth and Mary Pudney believe that B. triatomae is a good candidate for the biological control of Chagas disease, not least because of its capacity to form highly resistant cysts in vitro.     

Spermatogenesis and sperm ultrastructure in the polychaete genusOphryotrocha (Dorvilleidae)

The details of spermatogenesis and spermiogenesis are described forOphryotrocha puerilis. The ultrastructure of mature sperm is shown forO. puerilis, O. hartmanni, O. gracilis, O. diadema, O. labronica, andO. notoglandulata. Clusters of sixteen cells each are proliferated by two stem cells in each setigerous segment ofO. puerilis representing the very early stages of both oogenesis and spermatogenesis. In each spermatocyte-I cluster, the cells are interconnected by cytoplasmic bridges. Early, clusters are enveloped by peritoneal sheath cells. These transient gonad walls break down prior to meiosis. The meiotic processes may start in the clusters with the cells still interconnected, or during breakdown of the original cluster, giving rise to smaller subclusters of both spermatocytes I and spermatocytes II with various numbers of cells. Finally, spermatid tetrads are present. As spermiogenesis progresses, the tetrads disintegrate. Golgi vesicles in both spermatocytes and spermatids contain electron-dense material, presumably preacrosomal. The acrosome is formed by such vesicles. In the six species studied here, the acrosomes appear to be of a similar overall structure but are of different shape. Centrioles are usually located beneath the acrosome. The distal centriole forms the basal body of a flagellum-like cytoplasmic process. The microtubules of these flagellar equivalents do not show a normal ciliar arrangement. The flagellar equivalent appears to be non-motile. InO. hartmanni and inO. notoglandulata, a flagellar equivalent is missing. Microtubules originating from the proximal end of the distal centriole stretch to the nuclear envelope. This feature appears to be especially conspicuous inO. puerilis and inO. labronica. InO. labronica and inO. notoglandulata, bundles of microtubules paralleling the cell perimeter appear to stabilise the sperm. Various numbers of mitochondria are either randomly distributed around the nucleus or accumulate on one side, often directly under the acrosome. Parts of the present paper were presented at the 2^nd International Polychaete Conference, Copenhagen 1986 and at the 3^rd International Polychaete Conference, Long Beach, Ca. 1989.     

Larval development ofNeopisosoma neglectum werding, 1986 (Decapoda: Anomura: Porcellanidae) under laboratory conditions

The complete larval development of the porcellanid crabNeopisosoma negluctum Werding, 1986, was studied under laboratory conditions. At 27°C, the megalopa appeared after 9 days. The development consists of a transitory prezoea, two zoeal stages and a megalopa stage. The larvae exhibit telsonal features which places them in thePetrolisthes-group of porcellanid larvae. Larval morphology gives no additional support for the status ofNeopisosoma as an independent genus.     

Determination of the trophic state by qualitative and quantitative phytoplankton analysis in two gravel pit lakes

The phytoplankton of two gravel pits with comparable nutrient concentrations but different chlorophyll-a concentrations and phytoplankton biovolume was investigated qualitatively and quantitatively over a period of two years. This study deals with the phytoplankton-rich ‘Rotter See’ and the phytoplankton-poor ‘Paulsmaar’, both South of Cologne. The trophic state of both lakes was determined comparatively according to Ryding &; Rast (1989) and the categories used by Brettum (1989). The results were compared with each other. The trophic lake index according to Hörnström (1981) was modified slightly and subsequently determined for both lakes. A combination of qualitative and quantitative phytoplankton analysis made a proposal of a rehabilitation for the Rotter See possible.